Various types of silencing devices have been used to reduce or eliminate noise created when compressed gas is vented. Often, the compressed gas is being vented from a machine in an industrial setting. The noise that vented gas makes is harmful to the human ear and can cause hearing loss over time, creating a health hazard for workers.
One method of noise reduction of compressed gas is disclosed in U.S. Pat. No. 4,346,780. Here, pressurized gas is removed from pipes while the pipes under-go a zinc plating process. A purging device consists of a receptacle, a mouthpiece, and a placement means. The receptacle is a housing with a top, a bottom, at least two sides, and a substantially empty interior. The receptacle has an inlet port in one side, and an outlet port through the top of the receptacle. A deflection sheet extends from the top of the housing into the interior. A flexible curtain is suspended in the interior of the housing, and hangs vertically from the deflection sheet. A noise attenuator is placed at one end of the outlet port, opposite the top of the housing.
A mouthpiece has two open ends. One open end attaches to the housing at the inlet port, such that an open path exists from the mouthpiece, through the housing into the interior. A placement means is positioned on the outside of the housing and holds the mouthpiece.
A pipe is fitted into the mouthpiece. Steam is blown through the pipe. The vapors flow through the pipe, into the mouthpiece, and further into the interior of the receptacle. Vapors contact the deflection sheet, and flow down the length of the flexible curtain toward the bottom of the housing. Vapors continue to flow under the flexible curtain, and upwards along the length of the flexible curtain, toward the outlet port. Vapors then exit the housing through the outlet port, then flowing through the noise attenuator.
This configuration is disadvantageous noise reduction for several reasons. First, the receptacle can only accommodate one pipe at a time. Each plating station would require its own purge. Also, each time a new pipe is purged, the purging equipment must be disconnected from the plated pipe and reconnected to the new pipe requiring plating, slowing down the over-all production time. Furthermore, the purging device also is detrimental because it can create back-pressure. The compressed gas must be blown through the pipe by a fan. The short flow path and small noise attenuator allow back pressure to build up in the receptacle.
A sound diffuser is disclosed in U.S. Pat. No. 4,821,839. The diffuser has a housing with a top and a bottom. Sound-absorbing panels are constructed at different heights. The panels sit upright inside the housing and are attached to the bottom of the housing. Noise enters one end of the diffuser and travels over the panels toward the other end. As noise passes over the panels, it is absorbed.
While the sound diffuser incorporates sound-absorbing techniques, it is not adapted for use in an industrial environment. Specifically, this diffuser has no mechanisms or features that accommodate compressed gas removal. Also, the diffuser only accommodates one noise source.
A method for muffling compressed air from pneumatic tools is disclosed in U.S. Pat. No. 5,233,521. This method uses heat shrink tubing. A pneumatic tool exhausts compressed gas. Heat shrink tubing is disposed around the pneumatic tool. The tubing is then shrunk to fit the tool. When shrinking, a space is left between the tool and the tubing, leaving a passageway for the compressed gas to flow through. As the compressed gas flows away from the tool through the passageway, the heat shrink tubing also absorbs noise made by the compressed gas.
While this method removes compressed gas and absorbs noise, it is specifically adapted to pneumatic tools. Using heat shrunk tubing is only practical when the noise source is small. Also, heat shrunk tubing must be removed and reapplied each time the tool might need repair or maintenance work.
Another compressed air silencer is disclosed in U.S. Pat. No. 5,563,382. The silencer has a housing, with a top end, a bottom end, and four sides. An inlet port creates an open path through one side of the housing. An outlet port creates an open path through one side of the housing and is located at the side opposite the inlet port. Singular-piece baffles extend from the housing toward the open path. A silencing tube has a contained end and a free end. The contained end sits inside the outlet port, extending into the housing. The free end extends away from the housing.
A pipe expelling compressed gas fits into the inlet port. Compressed gas flows over the baffles. Noise is absorbed by the baffles during this flow. Gas exits the housing through the silencing tube, which provides further attenuation.
This silencer is disadvantageous. First, it can only accommodate one noise source at a time. Also, the small diameter of the outlet tube creates back-pressure at the exit, decreasing efficiency of the system and introducing a new noise source.